The “last mile” is a phrase in telecommunications, cable television and internet industries relating to the connection of retail customers (e.g., homes or offices) to the pertinent network (e.g., the telephone network or the internet). The “last mile” connections typically exhibit a bandwidth “bottleneck” limiting the rate of data delivery to the customers. Furthermore, “last mile” connections are expensive to upgrade due to the large number of such connections (i.e., relative to the number of connections between exchanges or routers).
Reference is now made to FIG. 1, which is a schematic illustration of a typical “last mile” connection which is known in the art. Such a typical “last mile” connection includes a building 10 a distribution point 20 and a central office 24. Building 10 includes, for example, eight apartments 121-128. Each of apartments 121-128 includes, for example, a respective one of computers 141-148 coupled with a respective one of modems 161-168 either directly or via a router or hub (not shown). Each one of modems 161-168 is coupled with distribution point 20 via a respective one of line connections 181-188 also known as “drops”. Each one of line connections 181-188 is, for example, a twisted pair of wires. Each one of line connections 181-188 may further be, for example, a coaxial cable. Line connections 181-188 are grouped together within a binder 22. Distribution point 20 along with line connections 181-188 and computers 141-148 constitute a communication system. Distribution point 20 is coupled with Central office 24 via a communication channel 26 (e.g., optical cable, wireless channel). The distance between building 10 and distribution point 20 is up to the order of hundreds of meters and typically up to 200 meters. The distance between distribution point 20 and central office 24 is up to the order of several kilometers.
It is noted that computers 141-148 are brought herein as an example only. Other devices require communication services (e.g., smart TV's, smartphones, IP phones, routers) may be coupled with the respective one of modems 161-168. Furthermore, building 10 may include offices rather than apartments. Additionally, the number of apartments or offices in building 10 may be different than eight (e.g. four, sixteen). Additionally, the distribution point may be connected to a plurality of private homes.
“G.fast” technology attempts to increase the data rate between the distribution point and the Customer Premise Equipment (CPE—such as modems, routers, hubs, computers, Smart TV's and the like) to the order of one Giga bits per second (i.e., 1 Gbps). Typically, the bandwidth of each twisted pair is between 100-200 Megahertz (MHz) and the number of twisted pairs per binder is between eight and sixteen. As a result of the high frequencies employed, a high degree of crosstalk interference exists between the different twisted pairs in the binder. In essence, due to the high level of crosstalk, the coupling between the distribution point and different CPE may be considered as a multiple access problem where a plurality of devices are coupled with the plurality of CPE's. Such a coupling or channel may be described in a matrix form where the entries in the matrix represent the different coupling factors.
Data transmission includes downstream transmission of data from the DP toward the CPE also referred to as downlink (DL). Data transmission also includes upstream transmission of data from the CPE toward the DP also referred to as uplink (UL). Furthermore, data transmission is divided into data frames, where each frame includes a plurality of time-slots each for transmitting a data symbols (i.e., a combination of bits is transmitted in each time-slot). Nevertheless, the terms ‘time-slot’ and ‘symbol’ are used herein interchangeably. In each frame, a portion of the symbols may be designated for downlink transmission and a portion of the symbols may be designated for uplink transmission. Frames may further be grouped in super-frames, where each super-frame includes a plurality (e.g., one the order of tens) of frames. Reference is now made to FIG. 2 which is a schematic of a super-frame, generally referenced 50, which is known in the art. Super-frame 50 includes a plurality of frames. The duration of super-frame 50 may in on the order of several milliseconds (ms) and typically 1 ms and each super-frame includes between 20 symbols and 40 symbols. Each frame, for example, frame 52, which corresponds to the second frame of super-frame 50, includes a plurality of time-slots, such as time-slot 54 for transmission of data symbols
U.S. Patent Application Publication 2011/0211503 to Che et al, entitled “Dynamic Allocation of Subframe Scheduling for Time Division Duplex Operation in a Packet-Based Wireless communication System” directs to a system and a method for dynamically allocating subframe of a communication frame for downlink transmission of for uplink transmission. In the system and method directed to by Che et al, radio frame defined as having a duration of 10 milliseconds. The radio frame is further subdivided into 10 subframes, each having a duration of 1 millisecond. Each subframe is further divided again into two slots, each having a duration of 0.5 milliseconds as shown. The frame further has three special fields to form a 1 millisecond special subframe. These special fields are the downlink pilot time slot, the guard period and the uplink pilot time slot. The other sub-frames may be allocated to either downlink transmission or uplink transmission according to certain rules. According to the system and method directed to by Che, there are seven TDD configurations of downlink and uplink subframe allocation patterns to be used. One of the configuration patterns, which would be chosen by a radio resource controller RRC and communicated to the User Equipment (UE) the base station, so the pattern selected is known to both the UE the base station. According to Che et al, a portion of the subframes are protected subframes allocated for only downlink or uplink transmission while the other portion of the subframes are flexible subframes which may be allocated to either downlink or to uplink transmission. The subframes are allocated according to one of two approaches for dynamic allocation. In the first approach, the subframe allocation is embedded in the flexible subframes when these are downlink subframes. According to the second approach, the allocation is made in the protected subframes.
U.S. Pat. No. 6,016,311 to Gilbert et al entitled “Adaptive Time Division Duplexing and Apparatus for Dynamic Bandwidth Allocation Within a Wireless Communication System” directs to an adaptive time division duplexing where the uplink and downlink bandwidth requirements are continuously monitored. Accordingly, the time slots of each frame are allocated for either uplink transmission or downlink transmission. According to one allocation process, a frame, which includes N consecutive time slots The First N1 time slots are dynamically configures for downlink transmissions only. The remaining slots are dynamically configured for uplink transmissions only. According to another allocation process, a frame, a plurality of adjacent time slots may interchangeably be allocated for downlink and uplink transmission.